Safety system incorporating a plurality of control switches

ABSTRACT

A safety system for signaling a malfunction of one of a plurality of elements in a driven instrumentality and for stopping the instrumentality. The system incorporates a control switch for each of the elements, each control switch having a signaling button that is movable between a retracted inactive position with respect to a case of the control switch and a projecting signaling position with respect to the case. A safety switch, which opens in response to a malfunction, is provided for each of the elements. Circuitry in the system linking the control switches, the instrumentality and the safety switches enables the instrumentality to operate when the buttons of all of the control switches are in their inactive positions, and all of the safety switches are closed. The opening of a safety switch, responsive to a malfunction, causes the button of the control switch associated with the open safety switch to move to its signaling position and causes the instrumentality to stop.

United States Patent [191 Sparks 1451 July 17, 1973 SAFETY SYSTEMINCORPORATING A PLURALITY OF CONTROL SWITCHES Buddy G. Sparks, Tulsa,Okla.

Frank W. Murphy Manufacturer, Inc., Tulsa, Okla.

Filed: Sept. 20, 1972 Appl. No.: 290,565

[75] Inventor:

[73] Assignee:

1,854,511 4/1932 Albertson ..317/9B 2,815,818 12/1957 Douglass PrimaryExaminer-James D. Trammell Attorney-D. Paul Weaver et al.

[57] ABSTRACT A safety system for signaling a malfunction of one of aplurality of elements in a driven instrumentality and for stopping theinstrumentality. The system incorporates a control switch for each ofthe elements, each control switch having a signaling button that ismovable between a retracted inactive position with respect to a case ofthe control switch and a projecting signaling position with respect tothe case. A safety switch, which opens in response to a malfunction, isprovided for each of the elements. Circuitry in the system linking thecontrol switches, the instrumentality and the safety switches enablesthe instrumentality to operate when the buttons of all of the controlswitches are in their inactive positions, and all of the safety switchesare closed. The opening of a safety switch, responsive to a malfunction,causes the button of the control switch associated with the open safetyswitch to move to its signaling position and causes the instrumentalityto stop.

13 Claims, 6 Drawing Figures Patehted Jul 17, 1973 3,746,926

3 Sheets-Sheet 5 FIG. 6

SAFETY SYSTEM INCORPORATING A PLURALITY OF CONTROL SWITCHES BACKGROUNDOF THE INVENTION In operating an instrumentality, it is desirable toprovide a system to stop the instrumentality in the event of amalfunction of one of the elements of the instrumentality and to providea signaling arrangement which will indicate the source of themalfunction. It is also desirable that the system be fail safe in thatthe instrumentality cannot operate in the event of a failure in thesignaling arrangement. While the prior art, as exemplified by US. Pats.Nos. l,097,680 and 2,740,953, shows signaling devices that are failsafe" in that a signal is created in response to the opening of acircuit, it does not show a signaling arrangement having a desiredreliability and flexibility.

SUMMARY OF THE INVENTION In accordance with a first aspect of thisinvention, a safety system is provided for signaling the malfunction ofone of a plurality of elements in a driven instrumentality and forstopping the instrumentality. The system includes a control switch and asafety switch for each of the elements, each safety switch beingopenable in response to a malfunction in its associated element. Eachcontrol switch includes a signaling device movable between an inactiveposition and a signaling position. A first electrical circuit extendsfrom a power source through the control switches to the instrumentalityto operate the instrumentality when all of the signaling devices are intheir inactive positions. A second electrical circuit extends from thepower source through each of the safety switches and from each safetyswitch to its associated control switch. The control switches and thefirst and second electrical circuits are so constituted that all of thesignaling devices are in their inactive positions when the first circuitand all of the second circuits are closed and an opening of a particularone of the safety switches operates to open the first circuit in thecontrol switch associated with the open safety switch to stop theinstrumentality and operates to move the signaling device of the controlswitch associated with the open safety switch to its signaling position.A third electrical circuit interconnects the control switches, and thecontrol switches and the third electrical circuit are so constitutedthat the remaining signaling devices are retained in their inactivepositions when the particular safety switch is opened. Thus, an openingof the particular safety switch causes a shutdown of the instrumentalityand also causes only the signaling device that is associated with theopen safety switch to be moved to its signaling position to signal thesource of the malfunction.

A second aspect of this invention relates to the construction of thecontrol switches. Each control switch has a solenoidformed of a'coil anda core that is magnetized in response to current flow through the coil.An armature is movably mounted to the control switch for movementbetween a first armature position wherein the armature is attracted toand bears against the core and a second armature position wherein thearmature is spaced from the core when no current is flowing through thecoil. An arm is movably mounted on the switch between a first armposition in which it is latched to the armature when the armature is inits first armature position and a second arm position when the armatureis in the second armature position. The signaling device takes the formof a button that is movable in a case enveloping the control switch andthat is in registry with the arm. When the arm is in its first armposition, the button is in engagement with the arm with the button inits inactive position, and a movement of the arm to the second armposition causes a movement of the button to its signaling position.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a section of the controlswitch showing the armature in its first armature position, the arm inits first arm position, and the button in its inactive position;

FIG. 2 is a view taken on the line 2-2 of FIG. 1;

FIG. 3 is a view taken on the line 33 of FIG. 1;

FIG. 4 is a view taken on the line 4-4 of FIG. 1;

FIG. 5 is a section of the control switch, similar to FIG. 1, butshowing the armature in its second armature position, the arm in itssecond arm position, and the button in its signaling position; and

FIG. 6 is a schematic representation of the electrical circuit of thesafety system.

DESCRIPTION OF THE PREFERRED EMBODIMENT The control switch 10, as shownin FIGS. 1 and 5, includes a base 12 of electrically insulative materialon which the switch components are mounted. Terminals 16, 18, 20, 22 and24 (FIG. 2) are mounted to the base 12 and extend downwardly thereof. Acase 26 is secured to the base 12 and extends upwardly thereof, the case26 enveloping those components of the switch, described below, thatextend upwardly of the base 12.

A solenoid 27, formed of a coil 28 and a core 34, is mounted to the base14 and extends upwardly thereof. A stand 30 is mounted to and extendsupwardly of the base 12 rearwardly of the coil 28. An armature 32 ispivotally mounted to the stand 30 in such a manner that a median portionof the armature, that extends forwardly of the stand 30, overhangs thecore 34 and is movable towards and away from the core. A tension spring36, interposed between a hook 38 on the stand 30 and the back of thearmature 32, yieldably urges the median portion of the armature 32 awayfrom the core 34.

A clevis 40 (see FIG. 3) is mounted to the base 12 forwardly of the coil28 and an arm 42 is pivoted on a pin 46 mounted to the clevis 40 forswinging movement toward and away from the coil 28. The arm 42 has afinger 48 that is movable between a leaf contact 50 that is inelectrically conductive connection with the termi nal 16 and a leafcontact 52 that is in electrically conductive connection with theterminal 18. A coil spring 54, that is entwined about the pin 46 and hasends bearing against the arm 42 and the clevis 40, yieldably urges thearm 42 forwardly away from the coil 28.

The front of the armature 32 extends through an aperture 56 in the arm42. An upwardly extending stop shoulder 58 on the top surface of thearmature 32 is engageable with the top surface of the aperture 56 tolimit the extent of forward movement of the arm 42 under the influenceof the spring 54 to a position, shown in FIG. 5, wherein the finger 48engages the contact 50 when the front of the armature is in a raisedposition under the influence of the spring 36.

A button 60 is movably mounted in a ferrule 62 in the case 14 forforward-rearward movement. The button 60 is located forwardly of and inalignment with the arm 42 and is yieldably urged rearwardly towards thearm 42 by a spring 64 that is interposed between the ferrule 62 and acollar 66 mounted on the button. The rearward movement of the button 60,in the manner described below, causes the button to bear against the arm42 and move the arm 42 rearwardly from the FIG. 5 position wherein thefinger 48 engages the contact 50. The rearward movement causes the topsurface of the aperature 56 to move along a rearwardly and upwardlyinclined upper surface 68 on the armature 32 to thus cam the armaturedownwardly about the pivotal connection between the armature and thestand 30 against the force of the spring 36 until the bottom surface ofthe aperture 56 is rearward of a shoulder 70 on the bottom surface ofthe armature. When the coil 28 is energized, as described below, thecoaction between the shoulder 70 and the bottom surface of the aperture56 acts as a latch to retain the armature 32 in the FIG. 1 positionwherein the finger 48 engages the leaf contact 52.

A contact 72, that is in electrically conductive connection with theterminal 20, is mounted to and extends upwardly of the base 12. Anelectrically conductive wire 74 extends between the contact 72 and abracket 76 (FIG. 4) that is mounted to the arm 42 to provide anelectrical current path between the arm 42 and the terminal 20.

Contacts 78 and 80, that are respectively in electrically conductiveconnection with the terminals 22 and 24, are mounted to and extendupwardly of the base 12. Wires 82 and 84, at the ends of the solenoidcoil 28, are respectively connected to the contacts 78 and 80.

A wire 86, incorporating a diode 88, extends between the contacts 50 and78. The diode 88 is so constructed as to permit current flow from thecontact 50 to the contact 78 while blocking or inhibiting current flowfrom the contact 78 to the contact 50.

FIG. 6 is a schematic illustration of a typical application of thecontrol switches 10, this being a safety control panel for aninstrumentality in the form of an engine driven pump wherein the controlswitches are utilized to indicate which of the elements of the engine orthe pump have failed to cause the engine, and thus the pump, to stop.The engine is operated by supplying electricity from a power source 88through a power switch 90, a line 92, a switch 93 of an ignition relay94, and an ignition coil 96 to sparkplugs 98. An engine oil pressuresafety switch 100, constructed to open in the event that the engine oilpressure becomes too low, is connected to the terminal 22 of a first ofthe control switches 10; an engine water temperature safety switch 102,constructed to open in the event that the engine water temperaturebecomes too high, is connected to the terminal 22 of a second of thecontrol switches 10; a pump suction pressure safety switch 104,constructed to open in the event that the pump suction pressure becomestoo low, is connected to the terminal 22 of a third of the controlswitches 10; and a pump discharge pressure safety switch 106,constructed to open in the event that the pump discharge pressurebecomes too low, is connected to the terminal 22 of a fourth of thecontrol switches 10. With the engine running and the safety switches100, 102, 104, I06 and 108 closed, the solenoid coils 28 of all fourcontrol switches 10 are energized by way of current flowing from theline 92 through a line 108 and the switches 100, 102, 104, and 106 tothe terminal 22 of each of the control switches 10. From each terminal22, the current flows through the solenoid coils 28 of each controlswitch 10 to energize the solenoid coils, thence to the terminals 24 ofthe control switches 10, and from the terminals 24 to ground via a line110,

In the normal condition of the control switches 10, with the enginedriven pump functioning properly, the buttons 60 of all four controlswitches 10 have been depressed rearwardly so that the arms 48 of allfour control switches 10 are retained by the coaction of the shoulderand the bottom surface of the aperture 56 in the FIG. 1 position withthe finger 48 in engagement with the contact 52 to thus provide acircuit between the terminals 18 and 20 of each of the control switches10. At this time, the spring 64 retains the button 60 in FIG. 1 positionwith its rearward end engaging the arm 42 and its front end within theferrule 62. The circuit between the terminals 18 and 20 enables currentto flow from the switch through a line 112, the switch terminals 20 and18 of the first of the control switches 10, a line 114, the switchterminals 20 and 18 of the second of the control switches 10, a line116, the switch terminals 20 and 18 of the third of the control switches10, a line 118, the switch terminals 20 and 18 of the fourth of thecontrol switches 10, a line 120, and terminal a of a single pole doublethrow running switch 122 to the ignition relay 94 to energize theignition relay 94 so that current may flow through the line 92 and theignition relay switch 93, as set forth above, to the ignition coil 96and the sparkplugs 98 of the engine.

Let us assume that, due to low oil pressure in the engine, the switchopens. This causes deenergization of the solenoid coil 28 of the controlswitch 10 associated with the switch 100. Deenergization of the coil 28enables the spring 36 to raise the front of the armature 32 away fromthe core 34 and to disengage the shoulder 70 from the bottom surface ofthe aperture 56 thereby enabling the spring 54 to move the arm 42forwardly to the FIG. 5 position wherein the top surface of theaperature 56 engages the shoulder 58 and the finger 48 is disengagedfrom the contact 52 and is in engagement with the contact 50. Theforward movement of the arm 42 to the FIG. 5 position pushes the button60 forwardly so that its front end is projected out of the ferrule 62 tothus act as a signal. The disengagement of the finger 48 from thecontact 52 opens the circuit between the switch 90 and the ignitionrelay 94 that includes the lines 112, 1 14, 116, 118, and 120 so as todeenergize the relay 94 and thus open the switch 93 to cut off the flowof current to the ignition coil 96 and the sparkplugs 98 and therebystop the engine which, in time, causes the remaining safety switchesI02, 104, and 106 to open.

The movement of the control switch 10 associated with the safety switch100 to the FIG. 5 position cnables current to flow from the line 112,through the contacts 72 and 50 and the diode 88 of this control switch10 to the contact 78 of this switch 10 and then through the coil 28 andthe terminal 24 of this control switch 10 to the line 110 to therebyagain energize the solenoid coil 28 of this switch 10. However, thiscontrol switch 10 remains in the FIG. 5 position with its button 60projecting forwardly despite the solenoid coil 28 having been energizedunder the force of its springs 54 with its armature 32 in its raisedposition away from its core 34 under the force of its spring 36.

The terminals 16 of the four control switches are connected by lines126, 128 and 130. Therefore, the current flowing into the contact 50 ofthe control switch 10 associated with the safety switch 100 will flowfrom the terminal 16 of this control switch 10, through the lines 126,128 and 130, to the terminals 16 of the other control switches 10. Fromthe terminals 16 of these other control switches 10 current flowsthrough their diodes 88, their contacts 72, their coils 28, and theirterminals 24 through the line 110 to ground so that the coils 28 ofthese other control switches 10 will remain energized after the safetyswitches 102, 104 and 106 have opend due to the engine shutdown to keepthe buttons 60 of these other switches 10 retracted within theirferrules 62.

Similarly, the opening of safety switch 102 due to an unsafe rise in theengine water temperature, the opening of the safety switch 104 due tothe lowering of the pump suction pressure, or the opening of the safetyswitch 106 due to the lowering of the pump discharge pressure causes thebutton 60 of the control switch 10 associated with the opened safetyswitch to be projected outwardly of its ferrule 62 while the remainingbuttons 60 remain retracted within their ferrules 62.

From the foregoing, it can be seen that the construction of the controlswitches 10 and the circuitry of FIG. 6 provide a system wherein thecontrol switches 10 operate to shut off the engine in the event of amalfunction causing an opening of one of the safety switches 100, 102,104, 106 with the projecting button 60 signaling the particularmalfunction. The running switch 122 may now be moved from its closed onposition at terminal a to its open off position at terminal b to ensurethat no current will flow to the engine ignition coil 96 and the enginesparkplugs 98 and the malfunc tion can be corrected. A line 132 extendsfrom the terminal 16 of the control switch 10 associated with the safetyswitch 106 to the terminal b of the running switch 122 and a line 134extends from this terminal b to the line 92. Thus, when the switch 122is in its of position, current flows through the lines 132, 130, 128 and126 to the terminals 16 of all of the control switches 10 and thencethrough the diodes 88, the contacts 78, the coils 28, the terminals 24and the line 110 to ground to thereby retain all of the coils 28energized despite the movement of the running switch 122 to its ofposition. The pushbutton 60 that had been projected out of its ferrule62 to signal the malfunction may now be pushed rearwardly to therebypush the arm 42 rearwardly until the armature 32 is latched by theshoulder 70 in the FIG. 1 position with the core 34 of the energizedcoil 28 retaining the armature in the latched FIG. 1 position. After themalfunction has been corrected, the switch 122 may be moved to its on"position to start the operation of the engine. This arrangement providesa fail safe system in that the engine cannot run unless all the circuitsfrom the power source 88 are complete to thus ensure reliability of thecontrol system against loose or broken electrical connections. In theevent of an open circuit anywhere between the power source 88 and thelines passing through the solenoid coils 28, the engine will notfunction, and the buttons 60 will be projected out of their ferrules 62to signal a malfunction.

It is noted that the energization of the coils 28 to magnetize the cores34 do not act to move the armatures 32 downwardly against the cores, butmerely retain the armatures against the cores after they have beenmanually forced against the cores by rearward manual movement of thebuttons 60. Therefore, the system has the advantage of being able to usea relative low voltage power system.

I claim:

1. A safety system for signaling a malfunction of one of a plurality ofelements in a driven instrumentality and for stopping theinstrumentality comprising: a sep arate control switch for each of saidplurality of elements; a signaling device in each of said controlswitches movable between an inactive position and a signaling position;a first electrical circuit extending from a power source through saidcontrol switches to said instrumentality; a safety switch associatedwith each of said elements adapted to open in the event of a malfunctionin its associated element; a second electrical circuit extending fromthe power source through each of said safety switches and from eachsafety switch to its associated control switch; said control switchesand said first and second electrical circuits being so constructed andarranged as to maintain all of the signaling devices in their inactivepositions when said first circuit and all of said second circuits areclosed and to cause an opening of a particular safety switch to open thefirst circuit in the control switch associated with the open safetyswitch andto move the signaling device associated with said particularsafety switch from its inactive to its signaling position; and a thirdelectrical circuit interconnecting the control switches; said controlswitches and said third electrical circuit being so constructed andarranged that the remaining signaling devices are retained in theirinactive positions when said particular safety switch is opened.

2. The system according to claim 1 wherein the con- 7 trol switches areso constructed that the signaling devices are manually movable fromtheir signaling to their inactive positions; and wherein the controlswitches and said third electrical circuit are so constructed andarranged that the signaling device in its signaling position is retainedin its inactive position when it is moved to its inactive position fromits signaling position.

3. The system according to claim 2 further comprising: aninstrumentality running switch, interposed in said first circuit betweenthe control switches and the instrumentality, movable between a closedposition wherein the instrumentality may be operated and an openposition wherein the instrumentality is precluded from operation; andwherein the instrumentality running switch and the third electricalcircuit are so constructed and arranged that the signaling device in itssignaling position is retained in its inactive position when it is movedto its inactive position from its signaling position'regardless ofwhether the running switch is in its closed or open position.

4. The system according to claim 1 wherein a case envelopes at least apart of each of said control switches; and wherein each of saidsignaling devices comprises a button movably mounted in each of saidcases between a retracted position wherein it is in said inactiveposition and a projecting position wherein it is in said signalingposition.

5. The system according to claim 4 wherein each of said buttons ismanually movable from its projecting position to its retracted position;and wherein the control switches and said third electrical circuit areso constructed and arranged that the button in its projecting positionis retained in retracted position when it is moved to its retractedposition from its projecting position.

6. The system according to claim further comprising: an instrumentalityrunning switch, interposed in said first circuit between the controlswitches and the instrumentality, movable between a closed positionwherein the instrumentality may be operated and an open position whereinthe instrumentality is precluded from operation; and wherein theinstrumentality running switch and the third electrical circuit are soconstructed and arranged that the button in its projecting position isretained in its retracted position when it is moved to its retractedposition from its projecting position regardless of whether the runningswitch is in its closed or open position.

7. The system according to claim 1 wherein each of said control switchescomprises: a first terminal, a second terminal, a third terminal, afourth terminal and a fifth terminal; a solenoid having a coil and acore; a first electrically conductive means interposed between saidfourth terminal and one end of said coil; a second electricallyconductive means interposed between said fifth terminal and the otherend of said coil; an armature movably mounted between a first armatureposition wherein the armature is attracted to and bears against the corepursuant to electric current flowing through the coil and a secondarmature position wherein the ar mature is spaced from the core when noelectric current is flowing through the coil; afirst spring meansyieldably urging the armature to said second armature position; a firstcontact in electrically conductive connection with said first terminal;a second contact spaced from said first contact, in electricallyconductive connection with said second terminal; an arm, having a fingerlocated between said contacts, mounted for movement between a first armposition wherein the finger is in engagement with said second contactand a second arm position wherein the finger is in engagement with saidfirst contact; a second spring means yieldably urging the arm to saidsecond arm position; cooperative latching means on said armature andsaid arm so constructed and arranged as to retain the arm in said firstarm position when the armature is in said first armature position and topermit movement of the arm to said second arm position under theinfluence of said second spring means when the armature is moved fromsaid first armature position to said second armature position under theinfluence of said first spring means; stop means inteposed between saidarmature and said arm to retain the arm in said second arm position whenthe arm is moved to said second arm position under the influence of saidsecond spring means; a third electrically conductive means interposedbetween said third terminal and saidarm; a fourth electricallyconductive means interposed between said first terminal and said firstelectrically conductive means so constituted as to permit current flowfrom said first terminal to said first electrically conductive means andto inhibit current flow from said first electrically conductive means tosaid first terminal; a case enveloping at least a part of the controlswitch; a button, in registry with the arm, mounted to the case formovement between a first button position wherein the button is retractedwith respect to the case and wherein the button is in engagement withthe arm while the arm is in said first arm position and a second buttonposition wherein the button is projecting with respect to the case andwherein the button is in engagement with the arm while the arm is insaid second arm position, said button constituting said signalingdevice, said first button position constituting said inactive positionof the signaling device, and said second button position constitutingsaid signaling position of the signaling device; and a third springmeans yieldably urging the button to said first button position; whereinsaid first electrical circuit comprises: an electrical connectionbetween said power source and the third terminal of a first of saidcontrol switches; an electrical connection between the second terminalof a second of said control switches and said instrumentality; andelectrical connections extending in series between the second terminalsof each of the control switches, excepting said second control switch,and the third terminal of another control switch; wherein said secondelectrical circuit comprises: an electrical connection between each ofsaid safety switches and the fourth terminal of its associated controlswitch; and an electrical connection between the fifth terminal of eachcontrol switch and the power source; and wherein said third electricalcircuit comprises: electrical connections extending in series betweenthe first terminals of each of the control switches.

8. The system according to claim 7 further comprising: aninstrumentality running switch, interposed in said first circuit betweenthe control switches and the instrumentality, movable between a closedposition wherein the instrumentality may be operated and an openposition wherein the instrumentality is precluded from operation; andwherein said third electrical circuit comprises: an electricalconnection between one of said first terminals and the power source whenthe running switch is in said open position.

9. A control switch comprising: a first terminal, a second terminal, athird terminal, a fourth terminal, and a fifth terminal; a solenoidhaving a coil and a core; a first electrically conductive meansinterposed between said fourth terminal and one end of said coil; asecond electrically conductive means interposed between said fifthterminal and the other end of said coil; an armature movably mountedbetween a first armature position wherein the armature is attractedtovand bears against the core pursuant to electric current flowingthrough the coil and a second armature position wherein the ar mature isspaced from the core when no electric current is flowing through thecoil; a first spring means yieldably urging the armature to said secondarmature position; a first contact in electrically conductive connectionwith said first terminal; a second contact, spaced from said firstcontact, in electrically conductive connection with said secondterminal; an arm, having'a finger located between said contacts, mountedfor movement between a first arm position wherein the finger is inengagement with said second contact and a second arm position whereinthe finger is in engagement with said first contact; a second springmeans yieldably urging the arm to said second arm position; cooperativelatching means on said armature and said arm so constructed and arrangedas to retain the arm in said first arm position when the armature is insaid first armature position and to permit movement of the arm to saidsecond arm position under the influence of said second spring means whenthe armature is moved from said first armature position to said secondarmature position under the influence of said first spring means; stopmeans interposed between said armature and said arm to retain the arm insaid second arm position wnen the arm is moved to said second armposition under the influence of said second spring means; a thirdelectrically conductive means interposed between said third terminal andsaid arm; afou'rth electrically conductive means interposed between saidfirst terminal and said first electrically conductive means soconstituted as to permit current flow from said first terminal to saidfirst electrically conductive means and to inhibit current flow fromsaid first electrically conductive means to said first terminal; a caseenveloping at least a part of the control switch; a button, in registrywith the arm, mounted to the case for movement between a first buttonposition wherein the button is retracted with respect to the case andwherein the button is in engagement with the arm while the arm is insaid first arm position and a second button position wherein the buttonis projecting with respect to the case and wherein the button is inengagement with the arm while the arm is in saidsecond arm position; anda third spring means yieldably urging the button to said first buttonposition.

10. The switch according to claim 9 wherein said fourth electricallyconductive means is comprised of a diode.

11. The switch according to claim 9 further comprising: a base; meansmounting the solenoid to the base; a stand mounted to and extendingupwardly of the base rearwardly of the solenoid; means pivotallymounting the armature to the stand so that a median portion of thearmature extends forwardly of the stand and overhangs the core and theback of the armature extends rearwardly of the stand; means mounting thefirst spring means so that it extends between the back of the armatureand the stand; an aperture in said arm through which the front of thearmature extends; a first shoulder on thebottom surface of the armature,said first shoulder coacting with the bottom surface of the aperture toconstitute said latching means; and a second shoulder on the top surfaceof the armature, located forwardly of said first shoulder, said secondshoulder coacting with the top surface of the aperture to constitutesaid stop means.

12. The switch according to claim 9 further comprising: a bracketmounted to said arm; and a third contact in electricallyconductiveconnection with said third terminal; and wherein said thirdelectrically conductive means comprises a wire extending between saidbracket and said third terminal.

13. The switch according to claim 9 further comprising: a third contactforming said first electrically conductive means, in electricallyconductive connection with said fourth terminal to which said one end ofthe coil is connected; and wherein said fourth electrically conductivemeans is comprised of a wire, incorporating a diode, that extendsbetween said first contact and said third contact.

1. A safety system for signaling a malfunction of one of a plurality ofelements in a driven instrumentality and for stopping theinstrumentality comprising: a separate control switch for each of saidplurality of elements; a signaling device in each of said controlswitches movable between an inactive position and a signaling position;a first electrical circuit extending from a power source through saidcontrol switches to said instrumentality; a safety switch associatedwith each of said elements adapted to open in the event of a malfunctionin its associated element; a second electrical circuit extending fromthe power source through each of said safety switches and from eachsafety switch to its associated control switch; said control switchesand said first and second electrical circuits being so constructed andarRanged as to maintain all of the signaling devices in their inactivepositions when said first circuit and all of said second circuits areclosed and to cause an opening of a particular safety switch to open thefirst circuit in the control switch associated with the open safetyswitch and to move the signaling device associated with said particularsafety switch from its inactive to its signaling position; and a thirdelectrical circuit interconnecting the control switches; said controlswitches and said third electrical circuit being so constructed andarranged that the remaining signaling devices are retained in theirinactive positions when said particular safety switch is opened.
 2. Thesystem according to claim 1 wherein the control switches are soconstructed that the signaling devices are manually movable from theirsignaling to their inactive positions; and wherein the control switchesand said third electrical circuit are so constructed and arranged thatthe signaling device in its signaling position is retained in itsinactive position when it is moved to its inactive position from itssignaling position.
 3. The system according to claim 2 furthercomprising: an instrumentality running switch, interposed in said firstcircuit between the control switches and the instrumentality, movablebetween a closed position wherein the instrumentality may be operatedand an open position wherein the instrumentality is precluded fromoperation; and wherein the instrumentality running switch and the thirdelectrical circuit are so constructed and arranged that the signalingdevice in its signaling position is retained in its inactive positionwhen it is moved to its inactive position from its signaling positionregardless of whether the running switch is in its closed or openposition.
 4. The system according to claim 1 wherein a case envelopes atleast a part of each of said control switches; and wherein each of saidsignaling devices comprises a button movably mounted in each of saidcases between a retracted position wherein it is in said inactiveposition and a projecting position wherein it is in said signalingposition.
 5. The system according to claim 4 wherein each of saidbuttons is manually movable from its projecting position to itsretracted position; and wherein the control switches and said thirdelectrical circuit are so constructed and arranged that the button inits projecting position is retained in retracted position when it ismoved to its retracted position from its projecting position.
 6. Thesystem according to claim 5 further comprising: an instrumentalityrunning switch, interposed in said first circuit between the controlswitches and the instrumentality, movable between a closed positionwherein the instrumentality may be operated and an open position whereinthe instrumentality is precluded from operation; and wherein theinstrumentality running switch and the third electrical circuit are soconstructed and arranged that the button in its projecting position isretained in its retracted position when it is moved to its retractedposition from its projecting position regardless of whether the runningswitch is in its closed or open position.
 7. The system according toclaim 1 wherein each of said control switches comprises: a firstterminal, a second terminal, a third terminal, a fourth terminal and afifth terminal; a solenoid having a coil and a core; a firstelectrically conductive means interposed between said fourth terminaland one end of said coil; a second electrically conductive meansinterposed between said fifth terminal and the other end of said coil;an armature movably mounted between a first armature position whereinthe armature is attracted to and bears against the core pursuant toelectric current flowing through the coil and a second armature positionwherein the armature is spaced from the core when no electric current isflowing through the coil; a first spring means yieldably urging thearmature to said second aRmature position; a first contact inelectrically conductive connection with said first terminal; a secondcontact spaced from said first contact, in electrically conductiveconnection with said second terminal; an arm, having a finger locatedbetween said contacts, mounted for movement between a first arm positionwherein the finger is in engagement with said second contact and asecond arm position wherein the finger is in engagement with said firstcontact; a second spring means yieldably urging the arm to said secondarm position; cooperative latching means on said armature and said armso constructed and arranged as to retain the arm in said first armposition when the armature is in said first armature position and topermit movement of the arm to said second arm position under theinfluence of said second spring means when the armature is moved fromsaid first armature position to said second armature position under theinfluence of said first spring means; stop means inteposed between saidarmature and said arm to retain the arm in said second arm position whenthe arm is moved to said second arm position under the influence of saidsecond spring means; a third electrically conductive means interposedbetween said third terminal and said arm; a fourth electricallyconductive means interposed between said first terminal and said firstelectrically conductive means so constituted as to permit current flowfrom said first terminal to said first electrically conductive means andto inhibit current flow from said first electrically conductive means tosaid first terminal; a case enveloping at least a part of the controlswitch; a button, in registry with the arm, mounted to the case formovement between a first button position wherein the button is retractedwith respect to the case and wherein the button is in engagement withthe arm while the arm is in said first arm position and a second buttonposition wherein the button is projecting with respect to the case andwherein the button is in engagement with the arm while the arm is insaid second arm position, said button constituting said signalingdevice, said first button position constituting said inactive positionof the signaling device, and said second button position constitutingsaid signaling position of the signaling device; and a third springmeans yieldably urging the button to said first button position; whereinsaid first electrical circuit comprises: an electrical connectionbetween said power source and the third terminal of a first of saidcontrol switches; an electrical connection between the second terminalof a second of said control switches and said instrumentality; andelectrical connections extending in series between the second terminalsof each of the control switches, excepting said second control switch,and the third terminal of another control switch; wherein said secondelectrical circuit comprises: an electrical connection between each ofsaid safety switches and the fourth terminal of its associated controlswitch; and an electrical connection between the fifth terminal of eachcontrol switch and the power source; and wherein said third electricalcircuit comprises: electrical connections extending in series betweenthe first terminals of each of the control switches.
 8. The systemaccording to claim 7 further comprising: an instrumentality runningswitch, interposed in said first circuit between the control switchesand the instrumentality, movable between a closed position wherein theinstrumentality may be operated and an open position wherein theinstrumentality is precluded from operation; and wherein said thirdelectrical circuit comprises: an electrical connection between one ofsaid first terminals and the power source when the running switch is insaid open position.
 9. A control switch comprising: a first terminal, asecond terminal, a third terminal, a fourth terminal, and a fifthterminal; a solenoid having a coil and a core; a first electricallyconductive means interpoSed between said fourth terminal and one end ofsaid coil; a second electrically conductive means interposed betweensaid fifth terminal and the other end of said coil; an armature movablymounted between a first armature position wherein the armature isattracted to and bears against the core pursuant to electric currentflowing through the coil and a second armature position wherein thearmature is spaced from the core when no electric current is flowingthrough the coil; a first spring means yieldably urging the armature tosaid second armature position; a first contact in electricallyconductive connection with said first terminal; a second contact, spacedfrom said first contact, in electrically conductive connection with saidsecond terminal; an arm, having a finger located between said contacts,mounted for movement between a first arm position wherein the finger isin engagement with said second contact and a second arm position whereinthe finger is in engagement with said first contact; a second springmeans yieldably urging the arm to said second arm position; cooperativelatching means on said armature and said arm so constructed and arrangedas to retain the arm in said first arm position when the armature is insaid first armature position and to permit movement of the arm to saidsecond arm position under the influence of said second spring means whenthe armature is moved from said first armature position to said secondarmature position under the influence of said first spring means; stopmeans interposed between said armature and said arm to retain the arm insaid second arm position wnen the arm is moved to said second armposition under the influence of said second spring means; a thirdelectrically conductive means interposed between said third terminal andsaid arm; a fourth electrically conductive means interposed between saidfirst terminal and said first electrically conductive means soconstituted as to permit current flow from said first terminal to saidfirst electrically conductive means and to inhibit current flow fromsaid first electrically conductive means to said first terminal; a caseenveloping at least a part of the control switch; a button, in registrywith the arm, mounted to the case for movement between a first buttonposition wherein the button is retracted with respect to the case andwherein the button is in engagement with the arm while the arm is insaid first arm position and a second button position wherein the buttonis projecting with respect to the case and wherein the button is inengagement with the arm while the arm is in said second arm position;and a third spring means yieldably urging the button to said firstbutton position.
 10. The switch according to claim 9 wherein said fourthelectrically conductive means is comprised of a diode.
 11. The switchaccording to claim 9 further comprising: a base; means mounting thesolenoid to the base; a stand mounted to and extending upwardly of thebase rearwardly of the solenoid; means pivotally mounting the armatureto the stand so that a median portion of the armature extends forwardlyof the stand and overhangs the core and the back of the armature extendsrearwardly of the stand; means mounting the first spring means so thatit extends between the back of the armature and the stand; an aperturein said arm through which the front of the armature extends; a firstshoulder on the bottom surface of the armature, said first shouldercoacting with the bottom surface of the aperture to constitute saidlatching means; and a second shoulder on the top surface of thearmature, located forwardly of said first shoulder, said second shouldercoacting with the top surface of the aperture to constitute said stopmeans.
 12. The switch according to claim 9 further comprising: a bracketmounted to said arm; and a third contact in electrically conductiveconnection with said third terminal; and wherein said third electricallyconductive means comprises a wire extending between said bracket aNdsaid third terminal.
 13. The switch according to claim 9 furthercomprising: a third contact forming said first electrically conductivemeans, in electrically conductive connection with said fourth terminalto which said one end of the coil is connected; and wherein said fourthelectrically conductive means is comprised of a wire, incorporating adiode, that extends between said first contact and said third contact.